Vertical type light emitting diode die and method for fabricating the same

ABSTRACT

A vertical type light emitting diode die and a method for fabricating the same is disclosed. A growth substrate is provided and an epitaxial layer is formed on the growth substrate. A metallic combined substrate is connected to the epitaxial layer. Then, the growth substrate is removed. Electrode units are formed on the top surface of the epitaxial layer. The epitaxial layer is divided into epitaxial dies according to the number of the plurality of electrode units. Each vertical type light emitting diode die formed in the abovementioned way includes the metallic combined substrate having a first metal layer and second metal layers. The first metal layer is combined with the two second metal layers by cutting, vacuum heating, and polishing, so as to enable the metallic combined substrate to have a high coefficient of thermal conductivity, a low coefficient of thermal expansion, and initial magnetic permeability.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a light emitting diode die and a methodfor fabricating the same, particularly to a vertical type light emittingdiode die having a high coefficient of thermal conductivity, a lowcoefficient of thermal expansion, and initial magnetic permeability anda method for fabricating the same.

Description of the Related Art

Light-emitting diodes (LEDs) used as light sources are fabricated usingthe semiconductor technology and formed by III-V group compoundsemiconductors. The LED operates based on a fact that electrons arecombined with holes in a semiconductor to produce photons. The LED isdifferent from the conventional light bulb working at a high temperatureof thousands of degrees and a fluorescent lamp using a high voltage toexcite an electron beam. Like a general element, a LED requires avoltage of 2˜4 V and works at a normal temperature. Thus, the life of aLED is longer than that of the conventional light source.

LEDs are divided into a horizontal structure and a vertical structure.Two electrodes of a horizontal LED are arranged at the same side of aLED chip. Two electrodes of a vertical LED are respectively arranged twosides of an epitaxial layer of the LED. Compared with the horizontalLED, the vertical LED has advantages of high brightness, fast cooling,small luminous decay, and high stability. No matter in structure,photoelectric parameter, thermal property, luminous decay, and cost, theheat dissipating effect of the vertical LED is much better than that ofthe horizontal LED. Due to the good heat dissipating property of thevertical LED, the heat generated by the chip is dissipated on time,thereby minimizing the attenuation in performance of the chip andphosphor. Thus, a LED features high brightness, fast cooling, smallluminous decay, and small drift of light color and provides morereliable stability.

However, LEDs are widely applied to many fields. For example, LEDs areapplied to a smart phone. When the smart phone overheats, the LED chipinstalled therein is also affected. The phenomena affect the substrateof the LED chip where a die is located. The substrate of the LED chip isconnected to the smart phone or other devices. If the substrate has ahigh coefficient of thermal expansion, the substrate is easily deformeddue to the variation of temperature, thereby influencing the lightingefficiency of the LED chip.

Accordingly, the present invention provides a vertical type lightemitting diode die and a method for fabricating the same to solve theabovementioned problems, whereby a substrate having a low cost, a highcoefficient of thermal conductivity, a low coefficient of thermalexpansion, and initial magnetic permeability is produced.

SUMMARY OF THE INVENTION

A primary objective of the present invention is to provide a verticaltype light emitting diode die and a method for fabricating the same,which provides a metallic combined substrate more suitable for a processof fabricating LEDs. The production yield of wire bonding of themetallic combined substrate is higher than that of a silicon substrate.The fabrication cost of the metallic combined substrate is lower thanthat of a general metal substrate. The metallic combined substrate has ahigh coefficient of thermal conductivity and a low coefficient ofthermal expansion, which greatly match the process of fabricating LEDs,whereby the installed LED stably maintains high lighting efficiencyrather than affects the substrate and deforms due to the variation oftemperature.

Another objective of the present invention is to provide a vertical typelight emitting diode die and a method for fabricating the same, whereinin addition to a high coefficient of thermal conductivity and a lowcoefficient of thermal expansion, the metallic combined substrate hasinitial magnetic permeability, such that a LED die transmits a microcurrent and generates electricity and light without connecting to avoltage source.

Further objective of the present invention is to provide a vertical typelight emitting diode die and a method for fabricating the same, whereinthe metallic combined substrate having initial magnetic permeability canovercome the problem with mass transfer of micro LEDs to massivelytransport or transfer LEDs in a fabrication process.

Yet another objective of the present invention is to provide a verticaltype light emitting diode die and a method for fabricating the same,wherein the heat-dissipating efficiency of the vertical type lightemitting diode die is higher than that of the horizontal type lightemitting diode die. After packaging the vertical type light emittingdiode die, a LED module with higher lighting efficiency is provided.

To achieve the abovementioned objectives, the present invention providesa vertical type light emitting diode die, which comprises a metalliccombined substrate comprising a first metal layer and two second metallayers respectively formed on a top surface and a bottom surface of thefirst metal layer, and the first metal layer is combined with the twosecond metal layers by cutting, vacuum heating, and polishing, so as toenable the metallic combined substrate to have a high coefficient ofthermal conductivity, a low coefficient of thermal expansion, andinitial magnetic permeability; and an epitaxial electrode layer formedon the metallic combined substrate.

The present invention also provides a method for fabricating a verticaltype light emitting diode die, which comprises: providing a growthsubstrate and forming an epitaxial layer on the growth substrate;providing a metallic combined substrate formed by cutting, vacuumheating, and polishing; forming a connecting metal layer on the metalliccombined substrate and connecting the metallic combined substrate to theepitaxial layer through the connecting metal layer; removing the growthsubstrate; forming a plurality of electrode units on a top surface ofthe epitaxial layer; and dividing the epitaxial layer into a pluralityof epitaxial dies on the metallic combined substrate according to thenumber of the plurality of electrode units.

In an embodiment of the present invention, the epitaxial electrode layerfurther comprises a connecting metal layer formed on the metalliccombined substrate; and at least one epitaxial die formed on theconnecting metal layer, the at least one epitaxial die is provided withan electrode unit thereon.

In an embodiment of the present invention, the first metal layercomprises an alloy of nickel and ferrum, and the second metal layercomprises copper.

In an embodiment of the present invention, the ratio of the second metallayer to the first metal layer to the second metal layer of the metalliccombined substrate in thickness is 1:2.5˜3.5:1.

In an embodiment of the present invention, the thickness of the metalliccombined substrate is less than or equal to 200 μm.

In an embodiment of the present invention, the cutting is laser cutting,and the polishing is chemical mechanical polishing or copper polishing.

In an embodiment of the present invention, the metallic combinedsubstrate uses the initial magnetic permeability to generate a microcurrent and transmit the micro current to the epitaxial electrode layer.

In an embodiment of the present invention, after the step of dividingthe epitaxial layer into the plurality of epitaxial dies, the connectingmetal layer and the metallic combined substrate are divided according tothe number of the plurality of epitaxial dies, and wire bonding andpackaging processes are performed on the plurality of epitaxial dies,the connecting metal layer and the metallic combined substrate to formlight-emitting diodes.

In an embodiment of the present invention, the light-emitting diodegenerates electricity and light without connecting to a voltage source.

In an embodiment of the present invention, the growth substrate isremoved using a chemical solution or a laser.

Below, the embodiments are described in detail in cooperation with thedrawings to make easily understood the technical contents,characteristics and accomplishments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a vertical type light emitting diode dieaccording to the first embodiment of the present invention;

FIG. 2 is a flowchart showing a method for fabricating a vertical typelight emitting diode die according to the first embodiment of thepresent invention;

FIGS. 3a-3f are diagrams schematically showing the steps of fabricatinga vertical type light emitting diode die according to the firstembodiment of the present invention; and

FIG. 4 is a diagram showing a vertical type light emitting diode dieaccording to the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In order to stabilize and enhance the lighting efficiency of LEDs andapply to a vertical type LED, the present invention improves a die and amethod for fabricating the same to change a coefficient of thermalexpansion of a substrate under the die and increase a coefficient ofthermal conductivity of the substrate. Thus, the deformation of thesubstrate does not influence the lighting efficiency of the LED athigher temperature later on. Owning to the special material of thesubstrate, the structure of the present invention can generateelectricity and light without connecting a voltage source.

Refer to FIG. 1. The vertical type light emitting diode die 10 comprisesa metallic combined substrate 12 and an epitaxial electrode layer 13.The epitaxial electrode layer 13 includes a connecting metal layer 14,at least one epitaxial die 16 and at least one electrode unit 18. In theembodiment, taking one epitaxial die 16 as example. The connecting metallayer 14 is formed on the metallic combined substrate 12. The epitaxialdie 16 is formed on the connecting metal layer 14. The electrode unit 18is formed on the epitaxial die 16.

Continuing from the abovementioned paragraph, the metallic combinedsubstrate 12 includes a first metal layer 122 and two second metallayers 124. The second metal layers 124 are formed on the top surfaceand the bottom surface of the first metal layer 122. The first metallayer 122 comprises an alloy of nickel and ferrum, wherein the ratio ofnickel to the alloy is 36%. The second metal layer 124 comprises copper.The ratio of the first metal layer 122 to the second metal layer 124 inthickness is 2.5˜3.5:1. In other words, the ratio of the second metallayer 124 to the first metal layer 122 to the second metal layer 124 inthickness is 1:2.5˜3.5:1. The present invention exemplifies a fact thatthe ratio of the first metal layer 122 to the second metal layer 124 inthickness is 3:1. For example, the best thickness of the first metallayer 122 is 60 μm and the best thickness of the second metal layer 124is 20 μm, but the present invention is not limited thereto. Thethickness of the metallic combined substrate 12 is less than or equal to200 μm.

Furthermore, the connecting metal layer 14 includes a contact layer 142,a reflection layer 144 and a current distribution layer 146. The contactlayer 142 is formed on the metallic combined substrate 12. Thereflection layer 144 is formed on the contact layer 142. The currentdistribution layer 146 is formed on the reflection layer 144. Thereflection layer 144 is provided with the epitaxial die 16 thereon. Inthe embodiment, the contact layer 14 is a P-type contact, and thereflection layer 144 is used as a reflector, and the currentdistribution layer 146 is a P-type GaP layer.

As mentioned above, the epitaxial die 16 further comprises a firstAlGaInP layer 162, a multi-quantum wells (MQWs) layer 164, a secondAlGaInP layer 166, and a GaAs layer 168. The first AlGaInP layer 162 isformed on the current distribution layer 146. The MQWs layer 164 isformed on the first AlGaInP layer 162. The second AlGaInP layer 166 isformed on the MQWs layer 164. The GaAs layer 168 is formed on the secondAlGaInP layer 166. The GaAs layer 168 is provided with the electrodeunit 18 thereon. In the embodiment, the first AlGaInP layer 162 is aP-type AlGaInP layer, and the second AlGaInP layer 166 is an N-typeAlGaInP layer, and the GaAs layer 168 is an N-type GaAs layer.

After describing the structure of the present invention, the method forfabricating the vertical type light-emitting diode die of the presentinvention is detailed as follows. Refer to FIG. 2 and FIGS. 3a-3f .Firstly, in Step S10 and FIG. 3a , a growth substrate 20 is provided,and an epitaxial layer 22 is formed on the growth substrate 20, and theepitaxial layer 22 is provided with a connecting metal layer 14 thereon.The connecting metal layer 14 includes a current distribution layer 146,a reflection layer 144, and a contact layer 142 from bottom to top. Inthe embodiment, the growth substrate 20 is a GaAs substrate. In Step S12and FIG. 3b , a metallic combined substrate 12 is provided, wherein themetallic combined substrate 12 is formed by laser cutting, vacuumheating, and polishing, such that the metallic combined substrate 12includes the first metal layer 122 and the two second metal layers 124respectively formed on the top surface and the bottom surface of thefirst metal layer 122. In the embodiment, the polishing is chemicalmechanical polishing (CMP) for the semiconductor fabrication process.Alternatively, a user chooses copper polishing. No matter CMP or copperpolishing, the copper surface of the second metal layer 124 is polishedto have surface roughness of 0.5˜0.01 μm such that the copper surface isused as a connection surface. The laser cutting uses UV-laser radiation(266 nm). The vacuum heating is performed under 100˜250 torr at 150˜250°C. for 10˜30 min. As a result, the stress of the metallic combinedsubstrate 12 is eliminated and the metallic combined substrate 12 isformed into a flat metal plate having a thickness of less than 200 μm.In Step S14 and FIG. 3c , the metallic combined substrate 12 isconnected to the epitaxial layer 22. The scope of the present inventionshould not be limited to the connection way that the metallic combinedsubstrate 12 is connected to the epitaxial layer 22. In Step S16, thegrowth substrate 20 is removed by a chemical solution after the metalliccombined substrate 12 is connected to the epitaxial layer 22. Thestructure without the growth substrate 20 is shown in FIG. 3d . In theembodiment, the chemical solution is a mixed solution of NH₄OH and H₂O₂.In addition to the chemical solution, laser cutting is alternativelyused, but the present invention is not limited thereto. In Step S18 andFIG. 3e , a plurality of electrode units 18 on the top surface of theepitaxial layer 22 by annealing. The alloy of Au and Ge is mixed with Auby annealing at a temperature of 360 degrees to form the electrode units18, wherein the ratio of the alloy of Au and Ge to Au is 2:3 in amount.Since FIG. 3e is a cross-sectional diagram, the present invention onlytakes two electrode layers 18 as an example for explanation. The presentinvention does not limit the number of the electrode layers 18. Thenumber of the electrode layers 18 is adaptable according torequirements. A plurality of electrode layers 18 may be used. In StepS20 and FIG. 3f , the epitaxial layer is divided according to the numberof the plurality of electrode units 18, such that an epitaxial die 16 isformed on each connecting metal layer 14. The epitaxial die 16 includesthe first AlGaInP layer 162, the multi-quantum wells (MQWs) layer 164,the second AlGaInP layer 166, and the GaAs layer 168. The bottommetallic combined substrate 12 includes the first metal layer 122 andthe second metal layers 124. Since FIG. 3f is also a cross-sectionaldiagram, the present invention only takes two epitaxial dies 16 as anexample for explanation, but the present invention is not limitedthereto. The epitaxial layer 22 may be divided into the epitaxial dies16 according to the number of the electrode units 18. The two epitaxialdies 16 and the two electrode units thereon are form one group. Theepitaxial layer 22 may be divided into the epitaxial dies 16 by chemicaletching or laser cutting, but the present invention is not limitedthereto.

In the vertical type light emitting diode die fabricated by theabovementioned method, the metallic combined substrate is different froma conventional silicon substrate. The production yield of wire bondingof the metallic combined substrate is higher than that of a siliconsubstrate. The fabrication cost of the metallic combined substrate islower than that of a general metal substrate made of Mo, and an alloy ofCu and W, or an alloy thereof. The metallic combined substrate of thepresent invention includes two metal layers and a mixed metal layerstacked. Thus, the metallic combined substrate is different from ageneral metal substrate. The metallic combined substrate of the presentinvention has a coefficient of thermal expansion of 5˜7 ppm/K,preferably 6.1 ppm/K@20° C. The metallic combined substrate of thepresent invention has a high coefficient of thermal conductivity. Themetallic combined substrate has a coefficient of thermal conductivity of20˜40 W/mK in a vertical direction and a coefficient of thermalconductivity of 170˜280 W/mK in a horizontal direction. The metalliccombined substrate is connected to the epitaxial layer through theconnecting layer, such that the metallic combined substrate is quite amatch for the epitaxial layer. The metallic combined substrate is thinenough. Without requiring a thinning process, the metallic combinedsubstrate not only possesses a low coefficient of thermal expansion, ahigh coefficient of thermal conductivity, a low cost, and a high yieldbut also easily connects to the epitaxial layer. In addition, themetallic combined substrate has the soft magnetic property of initialmagnetic permeability, wherein the initial magnetic permeability islarger than 2000. Thus, the metallic combined substrate uses the initialmagnetic permeability to generate a micro current and transmit the microcurrent to the epitaxial electrode layer. After assembling the verticaltype light emitting diode into a LED module, the LED module generateselectricity and light without connecting to a voltage source, so as tosatisfy the requirement for high power LEDs. On top of that, themetallic combined substrate is used as a permeance structure due to itssoft property and effectively applied to a production process. Sinceeach light emitting diode die has a very small volume, the lightemitting diode is difficultly manually held. Even the light emittingdiode is held by a machine, the machine must be very precise. It is verydifficult to transport a great number of the light emitting diode dies.However, a magnetic component, such as a tiny needle head, will beinstalled on a robot arm in the future. Thus, the robot arm can absorb agreat number of the vertical type light emitting diode dies with softproperties. In a fabrication process, the magnetic force is used toachieve the purpose of mass transfer, thereby improving thecompetitiveness for productions and overcoming the problem with masstransfer of micro LEDs.

Moreover, after dividing the epitaxial layer into the plurality ofepitaxial dies, the connecting metal layer and the metallic combinedsubstrate are divided according to the number of the plurality ofepitaxial dies. One epitaxial die and one electrode unit form one group.Wire bonding and packaging processes are performed on the plurality ofepitaxial dies, the connecting metal layer, and the metallic combinedsubstrate to form vertical type light-emitting diodes. The presentinvention does not limit the subsequent fabrication process and thestructures thereof, and the number of the structures. The abovementionedembodiment shows one group after a cutting process, but the present isnot limited thereto. A plurality of groups is alternatively formed. Thevertical type light emitting diode dies includes a plurality of groupseach having two epitaxial dies and two electrode units. The number ofthe groups is adaptable according to the requirement of a user. In anyenvironment, the quality of the vertical type light emitting diode dieof the present invention is better than that of a conventional verticallight emitting diode die due to the metallic combined substrate of thepresent invention having a low coefficient of thermal expansion. Themetallic combined substrate does not deform owning to the variation oftemperature. The present invention can stably maintain the high lightingefficiency of the light emitting diodes.

The present invention does not limit the structure of the epitaxialelectrode layer. Depending on how to cut the light emitting diode die,the number of the epitaxial dies on the connecting metal layer is one,two or more. As a result, the present invention provides a dualepitaxial structure, as shown in FIG. 4. The vertical type lightemitting diode die 30 comprises a metallic combined substrate 32 and anepitaxial electrode layer 33. The epitaxial electrode layer 33 includesa connecting metal layer 34, two epitaxial dies 36, and two electrodeunits 38. The connecting metal layer 34 is formed on the metalliccombined substrate 32, and the two epitaxial dies 36 are formed on theconnecting metal layer 34, and the two electrode units 38 arerespectively formed on the two epitaxial dies 36. The metallic combinedsubstrate 32 includes a first metal layer 322 and two second metallayers 324. The two second metal layers 324 are respectively formed onthe top surface and the bottom surface of the first metal layer 322. Theconnecting metal layer 34 includes a contact layer 342, a reflectionlayer 344, and a current distribution layer 346 from bottom to top. Thecontact layer 342 is formed on the metallic combined substrate 32. Thereflection layer 344 is provided with two epitaxial dies 36 thereon.Each epitaxial die 36 includes a first AlGaInP layer 362, amulti-quantum wells (MQWs) layer 364, a second AlGaInP layer 366, and aGaAs layer 368. The first AlGaInP layer 362 is formed on the currentdistribution layer 346. The GaAs layer 368 is provided with theelectrode unit 38 thereon. The structural content and the fabricationmethod of this embodiment is the same to those of the abovementionedembodiment. This embodiment is different from the abovementionedembodiment in that the vertical type light emitting diode die 30 of thisembodiment which shown in FIG. 4 is divided with a group of twoepitaxial dies 36, wherein the vertical type light emitting diode die 30is cut from to bottom until the connecting metal layer 34.

The embodiments described above are only to exemplify the presentinvention but not to limit the scope of the present invention.Therefore, any equivalent modification or variation according to theshapes, structures, features, or spirit disclosed by the presentinvention is to be also included within the scope of the presentinvention.

What is claimed is:
 1. A vertical type light-emitting diode diecomprising: a metallic combined substrate comprising a first metal layerand two second metal layers respectively formed on a top surface and abottom surface of the first metal layer, and the first metal layer iscombined with the two second metal layers by cutting, vacuum heating,and polishing, so as to enable the metallic combined substrate to have ahigh coefficient of thermal conductivity, a low coefficient of thermalexpansion, and initial magnetic permeability; and an epitaxial electrodelayer formed on the metallic combined substrate, one of the two secondmetal layer is located between the epitaxial layer and the first metallayer, the first metal layer comprises an alloy of nickel and ferrum,and the second metal layer comprises copper, a ratio of the second metallayer to the first metal layer to the second metal layer of the metalliccombined substrate in thickness is 1:2.5˜3.5:1, and a ratio of thenickel to the alloy is 36%.
 2. The vertical type light-emitting diodedie according to claim 1, wherein the epitaxial electrode layer furthercomprises: a connecting metal layer formed on the metallic combinedsubstrate; and at least one epitaxial die formed on the connecting metallayer, the at least one epitaxial die is provided with an electrode unitthereon.
 3. The vertical type light-emitting diode die according toclaim 1, wherein a thickness of the metallic combined substrate is lessthan or equal to 200 μm.
 4. The vertical type light-emitting diode dieaccording to claim 1, wherein the cutting is laser cutting, and thepolishing is chemical mechanical polishing or copper polishing.
 5. Thevertical type light-emitting diode die according to claim 1, wherein themetallic combined substrate uses the initial magnetic permeability togenerate a micro current and transmit the micro current to the epitaxialelectrode layer.